Mechanical jack



J. A. DUKE MECHANICAL JACK July 9, 1963 Filed June 4. 1962 2Sheets-Sheet 1 Illlllllul.:

INVENTOR Jacob A. Duke July 9, 1963 J. A. DUKE 3,096,967

MECHANICAL JACK Filed June 4, 1962 '2 sheets-sheet 2 IN V E N TOR JacobA. Duke United States Patent Office 3,096,967 Patented July 9, 1963Filed June 4, 1962, Ser. No. 199,743 1 Claim. (Cl. 254-126) Thisinvention relates generally to lifting devices, and more specifically tocertain new and useful improvements in the construction of `amechanically operated jack which incorporates safety features to enablethe jack to be used indefinitely without danger of collapse.

There have been many different designs of lifting device which providevarious degrees of mechanical advantage. Whilst these devices performeffectively for short periods of time, they are not generally consideredsuitable for supporting loads indefinitely. The safety of a jack underpermanent load is also a function of the base area of the jack, andpermanent stability demands a relatively high base to height ratio.

It is therefore a primary object of this invention to provide amechanically operated jack suitable for supporting continuous loads andincorporating safety features which will prevent collapse of the jack inthe event of thread failure of the screw drive which aotuates the jack.

It is a further object of this invention to provide an efiicientmechanical jack which is specially designed for supporting housetrailers and heavy duty vehicles.

It is a still further object of this invention to provide a mechanicaljack which may be operated remotely by rotation of the drive screw in ahorizontal axis.

It is yet a further object of this invention to provide a mechanicaljack of the above class which is rugged in construction, simple tooperate, and incorporates a secondary extension for adjusting themaximum lift thereof.

A full understanding of the details of the invention, together withfurther advantages, will become apparent by reference to the followingdetailed description of a preferred embodiment thereof, taken inconjunction with the attached drawings wherein:

FIG. l is a plan view of the jack which comprises my invention.

FIG. 2 is a front elevation of the jack showing the safety device in theengaged position.

FIG. 3 is a cross sectional end elevation taken along the line 3-3 ofFIG. l.

FIG. 4 is a fragmentary c-ross sectional plan View taken along the line4-4 of FIG. 2.

FIG. 5 is a fragmentary perspective View showing the slide mounting ofthe thrust block which supports the load.

Similar reference characters indicate corrmponding parts throughout theseveral views in the drawings.

Referring now to Ithe drawings in detail, the numeral 8 represents `aflat rectangular base which mounts two normally upstanding spaced apartside plates 9 which terminate upwardly with an `arc-uately formed edge1t). A pedestal 11 is formed by four vertical sleeve guides 12y whichform the corners of a square and have grooves 13 formed therealong `andextending towards each other to receive the slide plate 14 of a thrustblock 15 therebetween.

The thrust block lhas a vertical threaded hole 16 passing centrallytherethrough and has the two slide plates 14 extending therebeneath in aparallel spaced relationship as seen best in FIG. 5, of the drawing.Pour ears 17 project horizontally from the upper end of the thrust blockand are suitably drilled to receive pins 18 therethrough for pivotallymounting four downwardly diverging arms 19. Four further arms 20 arepivotally secured at their lower end by means of pins 21 and spacers 22to the inner side of 4the side plates 9. These further arms divergeoutwardly and upwardly and terminate in a pivotal relationship with theouter ends of the arms 19, the said ends being spaced apart by a spacerblock 23 having trunnions 24 projecting from cach end for pivotallymounting the ends of the converging arms 19 and 20. Stabilizing arms 25are secured by pins 26 to the diverging arms 19 at a point inwardlyspaced from their outermost ends. These arms converge downwardly andterminate centrally and inwardly of the side plates 9 where they arepivotally connected to a shaft 27 having a spacing sleeve 28 to maintainthe spaced relationship of the arms. The shaft 27 projects throughvertical slots 29 formed in each of the side plates 9 and is restrictedto vertical movement therewithin in response to raising and lowering thethrust block 15. A shaft 3() is rotatably supported in a bearing 31which is mounted on the pedestal 11 and the protruding ends of the shaftare threaded in opposite hands as indicated at 32 `and 33. The threadedends of the shaft extend through threaded holes 34 formed centrallythrough the spacer blocks 23 and terminate therebeyond lwith suitablesocket catches 35 for removably receiving a driving crank 36. It willthus be seen that rotation of the driving crank 36 in the socket catchat either end of the shaft 30 will cause the spacer blocks 23 to movetowards or away from each other and thereby causing the thrust block 15to rise or lower as required.

A bearing plate 37 is supported on a threaded post 38 which adjustablyprotrudes through the threaded hole 16 formed centrally and verticallythrough the thrust block 1S. This feature enables further adjustment inthe degree of lift available from the jack.

The safety catch device comprises four bars 39 secured to the outersides of the side plates and disposed from the lower corners thereof toextend upwardly in a converging manner as seen `best in FIG. 2. Thesebars are notched at 40 along their outer edge for engagement by theshaped ends 41 of locking levers 42 which are pivotally mounted at theirupper ends to the pins 26 which secure the stabilizing arms 25. Thelevers incorporate balancing arms 43 projecting normally therefrom suchthat the shaped ends 41 of the levers are constantly positioned adjacentthe notched bars 39 for immediate engagement therein in the event ofstructural failure of the jack. Catches 44 are pivotally mounted to thecentre of the locking levers 42 and have hooked end portions 45 whichmay be selectively engaged over the trunnions 24 as indicated in brokenlines in FIG. 2, so as to maintain the safety catch in the releasedposition whilst lowering the jack. The added safety afforded by theseautomatic locking levers will be quite apparent to those familiar withthe operation of mechanical type jacks.

Having described the invention with considerable partrcularity, itsho-uld be understood that various modifications may be made to theprecise detail thereof, without departing from the scope or spirit ofthe invention, as defined in the appended claim.

I claim:

A mechanical jack with safety locks, comprising, a base, side platesupstanding along opposite sides of the base, a pedestal mountedcentrally of the base and including four guides projecting upwardlytherefrom, a thrust block including downwardly extending plates forslideably engaging in said guides, two upper pairs of pivotally jointedarms mounted on opposite sides of the thrust block, two lower pairs ofarms pivotally mounted at their lower ends to said side plates,horizontally spaced trunnioned spacer yblocks pivotally connecting saidupper and lower pairs of `arms together, a shaft threaded in oppositehands at each end threadably engaging through the spacer blocks to causethe said 'blocks to converge and diverge with respect to each other inresponse to to the upper pairs of arms intermediate the length of thesaid arms, a stabilizing shaft extending through said plates, saidplates having vertical slots formed therein to receive the stabilizingshaft and restrict the saine to movement in a vertical plane, saidstabilizing bars oonverging downwardly and terminating with pivotalmounting on the stabilizing shaft, and a locking mechanism comprisingupwardly converging notched bars secured to the outer side of vthe sideplates, locking levers pivotally extending from said upper pairs ofjointed arms for selective engagement with the notched bars, and catcheson said locking levers for selectively maintaining said levers out ofengagement with said bars.

References Cited in the le of this patent UNITED STATES PATENTS1,470,830 Grant Oct. 16, 1923 1,486,797 Piper Mar. 11, 1924 1,652,821Fee Hern et al Dec. 13, 1927 FOREIGN PATENTS 617,313 Germany Apr. 16,1935

